1. Field of the Invention
The present invention relates to a pellicle for lithography and, more particularly, to a pellicle suitable for lithography using extreme ultraviolet light (EUV: Extreme Ultra-Violet) and a method for manufacturing the pellicle.
2. Description of the Related Art
Along with the increasingly higher integration of a semiconductor device, a pattern to be formed by lithography has been miniaturized. Nowadays, even a device having a pattern width of 45 nm or so is being put into practical use. Such a thin-line pattern can be realized by lithography using an ArF immersion method, a double exposure method or the like which are improved versions of a conventional excimer exposure technique.
With lithography based on such excimer exposure techniques as described above, however, it is considered difficult to cope with patterning requiring further miniaturization in which a pattern width is 32 nm or less. Hence, lithography using extreme ultraviolet light (EUV: Extreme Ultra-Violet) is now a focus of attention as a new exposure technique alternative to the above-described techniques.
For the practical application of an exposure technique using EUV light having a dominant wavelength of 13.5 nm, it is essential to develop a new resist, pellicle and the like, not to mention a light source. Among these, a significant progress has been seen in the development of the light source and resist. On the other hand, many technical problems that must be solved in order to realize a pellicle for EUV remain unsolved in the development of the pellicle.
A pellicle film to be provided in the pellicle for EUV is required to have high degrees of transmittance and chemical stability with respect to EUV light, needles to say a dust-preventing function for preventing foreign matter from adhering onto a photomask. The present situation is, however, that no solutions have yet been in sight to the problem of developing practical pellicle film materials superior in transmittance and chemical stability.
At present, there is not known any material transparent to light in a wavelength band having a dominant wavelength of 13.5 nm. On the other hand, silicon has a relatively high degree of transmissivity to light in this wavelength band and, therefore, has come to attract attention as a pellicle film material for EUV (see, for example, Shroff et al. “EUV pellicle development for mask defect control”, Emerging Lithographic Technologies X, Proc of SPIE Vol. 6151 615104-1 (2006): (non-patent document 1), U.S. Pat. No. 6,623,893 Specification: (patent document 1)).
However, the silicon used as a pellicle film in non-patent document 1 is a film deposited by means of sputtering or the like and is, therefore, inevitably amorphous. Consequently, the absorption coefficient of the film in an EUV region becomes high and, therefore, the transmissivity thereof becomes unavoidably low.
The material of the pellicle film disclosed in patent document 1 is also silicon and this silicon film is presupposed to be deposited by means of CVD or the like. Since the silicon film in this case inevitably results in an amorphous or polycrystalline film, the absorption coefficient thereof in the EUV region becomes unavoidably high.
In addition, a strong stress tends to be introduced into a film of silicon crystal, like the pellicle film disclosed in patent document 1 or non-patent document 1, formed using a sputtering method or a CVD method. This leads to another problem that the optical characteristics of the film tend to degrade or become nonuniform due to the stress.